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Persistent compressed expiring dict in Python, backed up by sqlite3 and pickle

Project description

A lightweight wrapper around Python’s sqlite3 database with a MutableMapping interface:

from expiringsqlitedict import SqliteDict
with SqliteDict('./my_db.sqlite') as mydict:
    mydict['some_key'] = any_picklable_object
    print(mydict['some_key'])  # prints the new value
    for key, value in mydict.items():
        print((key, value))
    print(len(mydict)) # etc... all dict functions work

Pickle is used internally by default to serialize the values, and zlib is used to optionally compress (on insertion, the value is compressed, and it’s stored compressed if the compressed value is smaller than uncompressed). Keys are arbitrary strings, values arbitrary pickle-able objects. This must be used within a context manager, and serialization can be overridden with your own. The database is wrapped with a transaction, and any exception thrown out of the context manager rolls back all changes.

This was forked off of sqlitedict in order to add auto-expiring functionality, and initially was quite similar to it. Version 2.0 splits of completely and takes the module into a complete rewrite, mostly to remove unnecesary Ptyhon 2 compatibility, simplify the API, completely enforce a context manager for typical cases, add full typing throughout, and use sqlite triggers for expiration cleanup.

This version also does not vacuum at all automatically. It did in previous versions, but this was kind of a silly behavior to put into the library itself. If you want your database file intermittently vacuumed, you should put such behavior into a crontab or use the sqlite3 module to do it yourself intermittently.

Features

  • Values can be any picklable objects (this can be customized to be as flexible as you need, through custom serializers)
  • Support for access from multiple programs or threads, with locking fully managed by sqlite itself.
  • A very simple codebase that is easy to read, relying on sqlite for as much behavior as possible.
  • A simple autocommit wrapper (AutocommitSqliteDict), if you really can’t handle a context manager and need something that fully handles like a dict.
  • Support for custom serialization or compression:
class JsonSerializer:
    @staticmethod
    def loads(data: bytes) -> Any:
        return json.loads(data.decode('utf-8'))

    @staticmethod
    def dumps(value: Any) -> bytes:
        return json.dumps(value).encode('utf-8')

with SqliteDict('some.db', serializer=JsonSerializer()) as mydict:
    mydict['some_key'] = some_json_encodable_object
    print(mydict['some_key'])

Installation

The module has no dependencies beyond Python itself.

Install or upgrade with:

pip install expiringsqlitedict

or from the source tar.gz:

python setup.py install

This module is a single file, so you could also easily import the module in your own tree, if your workflow needs that.

Testing

You may test this by running test.py with PYTHONPATH set to the current working directory. There is a convenience makefile to do this for you when you run:

make test

Documentation

Standard Python document strings are inside the module:

>>> import expiringsqlitedict
>>> help(expiringsqlitedict)

Comments, bug reports

expiringsqlitedict resides on github. You can file issues or pull requests there.


expiringsqlitedict is open source software released under the Apache 2.0 license. Version <2 Copyright (c) 2011-2018 Radim Řehůřek and contributors. All versions copyright (c) 2018-2021 Absolute Performance, Inc.

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